11月14日 美国哥伦比亚大学杜灵杰博士后学术报告：Quantum Spin Hall and Excitonic Condensation in Semiconductor Double Layers

报告题目: Quantum Spin Hall and Excitonic Condensation in Semiconductor Double Layers 
报 告 人: 杜灵杰 Columbia University
报告时间：2018年11月14日 （周三）10:00-11:30

报告地点：唐仲英楼B501 

报告内容简介：

Two-dimensional (2D) topological effects that interplay with electron-electron interactions have attracted lots of attention in the field of condensed matter physics. Quantum spin Hall (QSH) effect is such a typical topological effect. In this talk I will mainly present recent experimental studies of QSH effect in inverted InAs/GaSb quantum wells(QWs). In inverted InAs/GaSb QWs, using charge-neutral point (CNP) density as a tuning parameter, we observed two distinct QSH regimes: I), in dense limit in CNP, a single-particle hybridization gap opens, which hosts time-reversal-symmetry (TRS) QSH effect [1,2]; II), as dilute limit is approached, a spontaneous excitonic gap opens in the bulk, with the emergence of TRS-broken QSH effect where helical edges persist under high magnetic fields [1,3]. To clarify the interesting observation in regime II), we performed transport and THz measurements, and observed conclusive evidence for long-sought-after excitonic insulator(EI) [1]. The TRS-broken property of EI would be discussed. In the rest of my talk, I will discuss recent progresses of artificial graphene in nanopatterned GaAs QWs [4,5], which would offer exclusive tunability to 2D topological effects.